【作者】 赵勇铭；

【导师】 宋迎东；

【作者基本信息】 南京航空航天大学 ， 航空宇航推进理论与工程， 2009， 博士

【摘要】 本文针对承受多参数、非比例载荷的结构,开展其疲劳寿命预测模型以及疲劳试验谱编制方法的研究。采用有限元方法分析了简单带孔结构件和实际发动机机匣在不同多参数载荷作用下的应力应变分布特点,计算了构件在不同多参数循环载荷下的疲劳损伤分布。结果表明,在多参数载荷作用下,构件的最大应力点和最大疲劳损伤点的位置将随载荷变化而变化。针对多参数载荷下多点、单轴应力破坏模式的结构,提出了一种基于损伤等效原则的多参数疲劳试验谱编制方法。该方法先采用疲劳损伤计算方法求得多轴随机载荷作用下的初始裂纹萌生位置,然后对该点的应力应变历程进行雨流计数,对得到的应力应变循环按幅值进行分组,统计各组的载荷循环数并计算其损伤平均值;再对各组进行多参数循环载荷搜索,使该多参数循环载荷作用下结构的最大损伤点位置与原谱作用结果一致,且循环损伤等于组平均损伤;最后将各组所搜索到的多参数循环载荷按一定顺序连接起来,即得到多参数疲劳试验谱。试验结果表明:利用该方法所编制的疲劳试验谱的试验寿命分散带在2倍之内,编谱方法是有效的。建立了一种椭圆形式的多轴疲劳寿命预测模型。该模型考虑临界损伤平面上的最大剪切应变幅和法向应变程两个参数,并引入最大等效应力来考虑非比例循环附加硬化的影响,在单轴拉伸及扭转应力状态下退化为常规的单轴疲劳应变寿命模型。经不同材料的常幅多轴疲劳试验数据分析表明,所建立的疲劳寿命预测模型可同时适用于多轴比例与非比例循环加载,且具有较小的寿命分散带和标准差,预测精度高,材料适用范围较广,计算简便有效。针对多参数载荷下单点多轴应力破坏模式的结构,发展了一种基于多轴疲劳损伤等效的疲劳试验谱编制方法。在获得材料的多轴疲劳破坏模式后,采用多轴雨流计数法对主要损伤参量进行计数并分组统计;根据各组损伤值及主要损伤参量平均值进行搜索,使在搜索到的多参数循环载荷作用下的损伤值及主要损伤参量与各组统计平均值一致;最后将各组搜索到的循环载荷按一定的顺序连接起来,得到疲劳试验谱。试验结果表明:利用该方法所编制的疲劳试验谱的试验寿命分散带在2倍之间,提出的疲劳试验载荷谱编制方法是有效的。更多还原

【Abstract】 The fatigue life prediction model and the fatigue test spectrum formation of structures under multi-parameter and non-proportion loading are studied in this paper.The stress distributions of multi-hole thin cylinders and aeroengine cases under multi-parameter loading are analyzed by finite element method. The fatigue damage distributions of structures under multi-parameter loadings are calculated. The results show that the maximum stress point and the maximum damage position are changed with the multi-parameter loadings.Based on the damage equivalent principle, a new method which can be applied to structures with uniaxial stress failure modes under multi-parameter loadings is developed to create the multi-parameter fatigue test spectrum. At first the strain histories of the initial crack position are decomposed into a series of simple individual cycles by rain-flow counting method. The individual cycles are divided into several groups by strain amplitudes. In each group, the number of cycles is counted and the average damage value is computed. Then the multi-parameter cyclic loadings are searched in each group so that the maximum damage location under the loading is accord with the results under the effect of the original spectrum and the cyclic damage is equivalent with the average damage. The fatigue test spectrum is developed by linking these constant amplitude multi-parameter loadings. The experiment results show that the test life scatter band under the fatigue test spectrum which is compiled by this method is within 2 times compared with the original one, which proves the efficient of this method.A new multi-axial fatigue life prediction model, in which the parameters of the maximum shear strain amplitude and normal strain excursion are included and the influence of the additional cyclic hardening of maximum equivalent stresses are considered, is developed. The life prediction model developed can be degenerated to the traditional strain based life prediction model under uniaxial tension or torsion loadings. The experiment results show that the new life prediction model can be applied to both proportional and non-proportional loadings in different materials with smaller life scatter band and higher precision.Based on damage equivalent principle, a new method of creating the fatigue test spectrum is developed for the multi-axial stress destroying mode with single danger position under multi-parameter loadings. At first, the failure mode under multi-axial fatigue loadings is studied. The main damage parameters are counted by the multi-axial rain-flow counting method and divided into several groups. The damage value and the main damage parameters are searched in each group, so that these values under multi-parameter cyclic loadings are accord with the statistic average values of each group. The fatigue test spectrum could be created by linking these cycles with constant amplitudes. The experiment results show that the life scatter band under the fatigue test spectrum which is compiled by this method is within 2 times compared with the original one, which proves the efficient of the method developed for compiling the fatigue test specrum.更多还原